The present invention is generally related to angular sensing, and, more particularly, to a self-powered wireless sensor assembly for sensing angular position of the engine crankshaft in a vehicle, such as a land-based vehicle.
Engine angular position information, i.e., the angular position of the crankshaft, is needed for the control of engine operation, such as determining proper spark and fuel injection timing, etc. Each engine is equipped with a built-in, crankshaft sensor dedicated to engine operation. This sensor together with a toothed magnetic target comprises a crankshaft angle encoder. Its specifications vary from one engine model to another. The resolution typically is in the range of 3 to 60 pulses per revolution, and the angular accuracy is usually ±0.5°. These specifications are generally sufficient for engine operation. There is, however, another application for the crankshaft position information that requires a higher resolution and a better accuracy than the built-in crankshaft sensor system can provide. It is engine diagnostics and performance monitoring based on instantaneous engine speed variations.
The actual engine speed is not constant. Even in a steady state, an internal combustion (IC) engine generally exhibits cyclical speed variations attributable to the operation of its cylinders. Each individual cylinder slows the engine during its compression cycle and speeds it up during its power cycle.
In the field of vehicular diagnostics, accurate instantaneous engine speed information enables the detection and diagnosis of many engine problems, even subtle ones. See, for example, U.S. Pat. Nos. 4,539,841 and 4,520,658, respectively titled “Method For Determining Engine Cylinder Compression Pressure and Power Output” and “Method For Locating Engine Top Dead Center Position,” for some exemplary engine diagnostic applications that use accurate, high resolution crankshaft position information together with high accuracy and high resolution instantaneous engine speed information derived from the crankshaft position information. Presently, there is a limited choice in the ways of obtaining such information. For example, it is known that one can tap into the crank sensor wiring, or use a separate, intrusive sensing technique, such as mounting a wired sensor in the bell housing, permanently or just for the duration of the diagnostic procedure, to sense the rotation of the ring gear.
Shortcomings of the first approach for obtaining engine crankshaft position information may include burdensomely locating and gaining access to the crank sensor connector, the location of which connector typically varies from vehicle to vehicle. This generally results in incremental costs since even just a few additional minutes per vehicle cumulatively may add up to substantial costs when servicing a large number of vehicles. More importantly, the accuracy and resolution of the crankshaft position information in the majority of cases would not yield usable instantaneous engine speed information. Similarly, costly and time-consuming inefficiencies may arise with the second approach for obtaining crankshaft position information since intrusive sensing of crankshaft position is generally not conducive to quick and cost-effective servicing and/or diagnostics operations, and often requires costly vehicle modification.